Tapping Circles from the main Google+ screen brings you to the apps Circles interface. I can view the people in my Circles either alphabetically as a whole, or tap Circles at the top to view each of my Circles separately.
There is a Suggest People tab, and a search function so I can add new people to my Circles on the go. From within the Circles view, I can also add new Circles if I choose.
When I tap on the Photos button on the main Google+ app screen, I am presented with four thumbnails--From your circles, Photos of you, Your albums, and From your phone. Each one displays a slideshow of the available photos from the category.
At the upper right of the Photos screen there are also two icons, but these two icons are the two that appear at the bottom of the Places check-in or Google+ post entry screens. I can tap to take a new photo, or tap to add a photo from my iPhone or iPad.
I tapped on the "From your circles" thumbnail, and it opened up a screen with a bunch of smaller thumbnails of the photos that have been shared by various people within my Circles. Beneath each one is a little speech bubble square with a number next to it indicating how many comments have been left on that photo. This isn't my preferred method of finding photos from my Circles, but it is sort of interesting to be able to quickly identify which photos are generating the most discussion and jump in if I want.
Huddles is a Google+ feature that is unique to the mobile client. A Huddle is basically a group chat function. You can start a Huddle with an entire Circle or Circles, or invite specific individuals. Those who participate in the Huddle can all see and participate in the dialog going on among the group.
This can be useful for a group of friends trying to figure out where to meet up for dinner, or for a team of co-workers to chat about a project. I haven't yet figured out why Huddles aren't available on Google+ proper, though. There is a chat function within Google+, and Google+ has Hangouts to facilitate group video chats, but it seems to me that being able to start a Huddle with a Circle or group of individuals has as much or more value from my PC than it does from my iPhone.
Define "iPad Compatible"
One thing the Google+ iOS app is not is "iPad compatible". When the Google+ app first hit the Apple App Store it would only install on an iPhone or iPod Touch. Later, Google released a new "iPad compatible" version with much fanfare and hoopla.
The problem lies in defining "iPad compatible". Being able to install an iPhone app so that it shows up as an iPhone-sized square that won't orient in landscape mode is significantly different than being iPad compatible in my opinion. What Google meant when it said the Google+ app is compatible with the iPad is that it revised the iPhone app so it would work like every other iPhone app.
By that measure, the Facebook iOS app is "iPad compatible" too. It still sucks on an iPad. Is it functional? Yes. It will work. It is better than nothing. But, to see the difference between an iPhone app running on an iPad, and an actual iPad app try running the iPhone version of Skype on an iPad, then look at the actual iPad version.